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APPENDIX C Instruction Overview
C.3 Bit Manipulation Instructions (SETB, CLRB)
Some peripheral function registers include bits that are read differently than usual by a
bit manipulation instruction.
■
Read-modify-write Operation
By using these bit manipulation instructions, you can set only the specified bit in a register or RAM
location to "1" (SETB) or clear to "0" (CLRB). However, as the CPU operates data in 8-bit units, the actual
operation (read-modify-write operation) involves a sequence of steps: 8-bit data is read, the specified bit is
changed, and the data is written back to the location at the original address.
Table C.3-1 shows bus operation for bit manipulation instructions.
■
Read Destination on the Execution of Bit Manipulation Instructions
For some I/O ports and the interrupt request flag bits, the read destination differs between a normal read
operation and a read-modify-write operation.
●
I/O ports (during a bit manipulation)
From some I/O ports, an I/O pin value is read during a normal read operation, while a port data register
value is read during a bit manipulation. This prevents the other port data register bits from being changed
accidentally, regardless of the I/O directions and states of the pins.
●
Interrupt request flag bits (during a bit manipulation)
An interrupt request flag bit functions as a flag bit indicating whether an interrupt request exists during a
normal read operation, however, "1" is always read from this bit during a bit manipulation. This prevents
the flag from being cleared accidentally by writing the value "0" to the interrupt request flag bit when
manipulating another bit.
Table C.3-1 Bus Operation for Bit Manipulation Instructions
CODE
MNEMONIC
~
Cycle
Address bus
Data bus
RD
WR
RMW
A0 to A7
A8 to AF
CLRB dir:b
SETB dir:b
4
1
2
3
4
N+2
dir address
dir address
N+3
Next instruction
Data
Data
Instruction after next
1
1
0
1
0
0
1
0
1
1
0
0
Содержание F2 MC-8FX Family
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Страница 30: ...16 CHAPTER 1 DESCRIPTION 1 FPT 64P M23 FPT 64P M24 2 For the I O circuit type refer to 1 8 I O Circuit Type ...
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Страница 35: ...21 CHAPTER 2 HANDLING DEVICES This chapter gives notes on using 2 1 Device Handling Precautions ...
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Страница 39: ...25 CHAPTER 3 MEMORY SPACE This chapter describes memory space 3 1 Memory Space 3 2 Memory Map ...
Страница 43: ...29 CHAPTER 4 MEMORY ACCESS MODE This chapter describes the memory access mode 4 1 Memory Access Mode ...
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Страница 105: ...91 CHAPTER 8 INTERRUPTS This chapter explains the interrupts 8 1 Interrupts ...
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Страница 564: ...550 CHAPTER 29 EXAMPLE OF SERIAL PROGRAMMING CONNECTION ...
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Страница 599: ...585 Pin Function Index V2 LCD power supply driving pin 2 439 V3 LCD power supply driving pin 3 439 ...
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